Talk:Exponential integral

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There's something wrong with the final statement on the page. It reads

E_n(x) = \int_1^\infty \frac{e^{-xt}}{t}\, dt.

The left-hand side depends on 'n', but the right-hand side is independent of 'n'. The wolfram's site http://mathworld.wolfram.com/En-Function.html suggests this:

E_n(x) = \int_1^\infty \frac{e^{-xt}}{t^n}\, dt.

[edit] Numerical evaluation

Could anybody type a reference to the C++ code for efficient evaluation of Ei(z) with double-complex precision over all the compex plane? dima (talk) 05:32, 13 January 2008 (UTC)

[edit] cut of Ei(z): z<0 ok?

For the extension of Ei(z) to the complex values of z, we need to put cut somewhere. How about z<0? If no objections, I shall update the definition. dima (talk) 04:45, 5 February 2008 (UTC)